The small subunit of T4 terminase, gp16, in association with the large subunit, gp 17, is involved in the initiation of concatemer processing in packaging of the DNA. The monomer is 19 kD but is an apparently homogeneous oligomer on gels (about a 10 to 20mer). In conventional EM, the oligomers appear as rings. Mass measurements in the STEM indicate that the rings appear to be octamers or dimers of that. Stained specimens are being prepared to obtain more details of the structure of these oligomers.